1. Field of the Invention
The present invention relates to an axle assembly, and more particularly to a device for tuning a hydraulically actuated clutch assembly in the axle assembly.
2. Description of the Prior Art
Conventionally, differentials well known in the prior art, are arranged in a power transmission system of a motor vehicle to allow a pair of output shafts operatively coupled to an input shaft to rotate at different speeds, thereby allowing the wheel associated with each output shaft to maintain traction with the road while the vehicle is turning. Such a device essentially distributes the torque provided by the input shaft between the output shafts. However, these types of differentials known in the art as an open differentials, i.e. a differential without clutches or springs, are unsuitable in slippery conditions where one wheel experiences a much lower coefficient of friction than the other wheel; for instance, when one wheel of a vehicle is located on a patch of ice or mud and the other wheel is on dry pavement. In such a condition, the wheel experiencing the lower coefficient of friction loses traction and a small amount of torque to that wheel will cause a xe2x80x9cspin outxe2x80x9d of that wheel. Since the maximum amount of torque, which can be developed on the wheel with traction, is equal to torque on the wheel without traction, i.e. the slipping wheel, the engine is unable to develop any torque and the wheel with traction is unable to rotate. Thus, the necessity for a differential, which limits the differential rotation between the output shafts to provide traction on slippery surfaces, is well known.
A number of methods have been developed to limit wheel slippage under such conditions. Prior methods of limiting slippage between the side gears and the differential case typically use a friction clutch assembly between the side gear and the differential case. The frictional clutch is usually actuated by a hydraulic actuator including a hydraulic pump and a piston assembly including a hydraulic piston applying a compressive clutch engagement force to the frictional clutch assembly. The limited slip differential having the hydraulic clutch actuator needs to be tuned (or calibrated) in order to achieve desired application rate of torque transfer of the friction clutch assembly. Currently, tuning of the limited slip differential is achieved by providing a bleed groove of an appropriate cross-section in the piston. In order to adjust the differential tuning, the differential is disassembled and the piston is replaced to a new one with the bleed groove having different cross-section providing desired tuning.
Thus, the limited slip differentials of the prior art are not readily tunable, and the tuning procedure of the current limited slip differentials requires removing, disassembling and rebuilding thereof with the new hydraulic piston. This method is cumbersome, laborious and time consuming.
The present invention provides an improved readily tunable hydraulically controlled limited slip differential assembly permitting simple and quick tuning thereof without disassembling.
The differential assembly in accordance with the preferred embodiment of the present invention includes a rotatable differential case, a differential gearing rotatably supported in the differential case, a pair of opposite side gears in meshing engagement with the differential gearing to permit differential rotation thereof, a friction disk clutch assembly disposed within the differential case for selectively restricting differential action, and a hydraulic actuator assembly including a piston assembly and a bi-directional gerotor pump. The friction clutch assembly includes a number of alternating outer friction plates non-rotatably coupled to the differential case and inner friction plates splined to one of two opposite output shafts each drivingly coupled to the corresponding side gear. The piston assembly includes a hydraulic piston disposed in a piston housing forming a pressure chamber. The piston housing is provided with a removable bleed plug defining a flow restricting bleed passage. The bleed plug is accessible from the outside of the differential assembly without disassembling thereof through an access hole in the differential case. By appropriately selecting a flow area of the bleed passage, the limited slip differential assembly may be tuned to define application rate of torque transfer of the friction clutch assembly.
Therefore, the limited slip differential assembly in accordance with the present invention is a novel arrangement of the limited slip differential assembly that provides easy access to a bleed plug and permits quick installation/removal thereof without disassembling of the differential assembly. The method for tuning a limited slip differential assembly in accordance with the present invention solves the need for a solution to the problem of calibrating the application rate of the transfer torque of the limited slip differential assemblies without disassembling of the differential assembly in a simple, quick, efficient and inexpensive manner.